This application relates to devices for pivotally mounting a lens holder within the housing of a telescopic sight such as a riflescope and, in particular, to a pivot mount having opposing socket elements that can be sized to laterally-equalize friction forces imparted to the lens holder when it is pivoted within the housing.
Riflescopes typically include eyepiece and objective lenses positioned at opposite ends of a tubular housing. In variable optical power scopes, an erector lens positioned medially of the eyepiece and objective lenses is movable along a central longitudinal axis of the housing for adjustment of the optical power of the riflescope. An aiming reticle is positioned in the optical path of the rifle scope, typically between the erector lens and the eyepiece lens.
Because bullet trajectory, wind conditions, and the distance to the target can vary depending upon shooting conditions, quality riflescopes allow the shooter to compensate for such variations by a mechanism that adjusts the aim of the sight relative to the rifle on which it is mounted. The aiming adjustments are known as xe2x80x9cwindagexe2x80x9d and xe2x80x9choldoverxe2x80x9d and are typically accomplished by lateral movement of the erector lens within the housing to divert the optical path of the observed light before it reaches the reticle, as shown in U.S. Pat. Nos. 3,297,389 and 4,408,842 of Gibson. In these designs, a pivot end of a pivot tube that extends along the longitudinal axis is pivotally mounted to the interior of the housing. The erector lens is supported near a free end of the pivot tube opposite the pivot end. A marksman accomplishes adjustment of windage and holdover by turning a laterally protruding screw or other adjustment mechanism that drives the free end of the pivot tube laterally within the housing of the riflescope.
U.S. Pat. No. 4,408,842 of Gibson describes a half-socket pivot mount for a riflescope that includes a spring for urging a spherical end of the pivot tube against a conical socket surface formed in the housing. The conical socket surface helps to center the spherical end on the longitudinal axis. Because the spherical end of the pivot tube contacts the conical socket along only a small circular band, friction and wear are high at the contact area relative to full-socket pivot mounts (which have a much larger contact area). Also, as described below, the frictional forces may cause the spherical end to walk and become offcentered.
Riflescopes with full ball and socket pivot mounts for the erector lens tube have previously been proposed, as shown in U.S. Pat. No. 3,297,389 of Gibson and U.S. Pat. No. 3,918,791 of Perry. These prior art full ball and socket mounts employ no socket spring to hold the pivot assembly together, absorb rifle recoil, and enable smooth adjustment of the erector lens holder tube for windage and range elevation corrections. Spherical sockets also require tighter manufacturing tolerances to ensure a snug fit between the socket and the ball.
FIG. 1 shows a schematic side sectional view of a prior-art riflescope 100 including a half-socket pivot mount 106. With reference to FIG. 1, riflescope 100 includes a tubular housing 110 having an interior socket surface 114. A pivot tube 120 mounted within housing 110 includes a hemispherical pivot end 124 sized for a sliding fit against socket surface 114 and a free end 126 extending within the housing away from pivot end 124. For clarity, socket surface 114 and pivot end 124 are shown spaced apart. However, in practice, pivot end 124 is in sliding contact with socket surface 114. Socket surface 114 is shown in FIG. 1 as frusto-spherical in shape, but, as discussed above, it is also known to use a frusto-conical socket surface to help keep pivot mount 106 centered. A pivot spring (not shown) such as a wave spring or a set of coil springs biases hemispherical pivot end 124 against socket surface 114 in the direction shown by Fs. Pivot mount 106 is positioned proximal of an eyepiece end 130 of riflescope 100. However, it is also known to position a pivot mount near the objective end (not shown) of the riflescope.
In operation, a marksman adjusts the orientation of pivot tube 120 within housing 110 by turning adjustment knobs (not shown) that extend laterally from housing 110. The adjustment knobs apply adjustment forces FA to the free end 126 of pivot tube 120 and thereby cause the pivot tube 120 to rotate transversely of housing 110 in the direction indicated by arrows 140. Ideally, pivot tube 120 pivots about a pivot point 150 located on a longitudinal axis 156 of housing 110. However, in practice, the spring force FS and pivotal movement results in lateral frictional forces Ff1 and Ff2. These lateral frictional forces Ff1 and Ff2 can cause the pivot end 124 to xe2x80x9cwalkxe2x80x9d out of alignment relative to housing 110 such that the center of curvature of pivot end 124 no longer falls on longitudinal axis 156. This walking effect can affect the aim of riflescope 100. Walking can also cause the pivot spring to compress and further increase the friction and wear at the socket surface 114.
Thus there exists a need for a riflescope with a pivot mount that is more durable, more accurate, and less susceptible to binding and walking than prior art pivot mounts.
A telescopic sight in accordance with the present invention includes an elongate housing having a bore extending through the housing along a central longitudinal axis of the housing. A pivot mount of the telescopic sight includes a fixed half-socket rigidly mounted to the housing within the bore and a movable half-socket slidably positioned within the bore opposing the fixed half-socket. A lens holder is disposed within the bore and includes a pivot end pivotally seated between the fixed and movable half-sockets for rotation about a pivot point. A resilient member biases the movable half-socket toward the fixed half-socket so as to capture the pivot end between the fixed half-socket and the movable half-socket while allowing pivoting movement of the lens holder therebetween. The lens holder extends within the bore generally along the longitudinal axis and terminates in a free end medially of an eyepiece end and an objective end of the housing, where it can support an erector lens assembly. The free end of the lens holder is engaged by a manual adjustment mechanism that is operated to drive the lens holder to rotate about the pivot point transversely of the longitudinal axis.
The fixed and movable half-sockets contact the pivot end at respective first and second pivot interfaces at which rotation of the lens holder about its pivot end generates respective first and second lateral frictional force components. The pivot contact surfaces are preferably sized and shaped so that the first and second lateral frictional force components substantially equalize each other and thereby prevent the lens holder from walking relative to the housing of the telescopic sight.
Additional aspects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof, which proceeds with reference to the accompanying drawings.